DTC 44

CIRCUIT DESCRIPTION
The Engine Control Module (ECM) supplies a voltage of about 0.45 volt between terminals "D-6" and "D-7". (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volts.) The O2 sensor varies the voltage within a range of about 1 volt if the exhaust is rich, down through about 0.10 volt if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is below about 360°C (600°F) An open sensor circuit or cold sensor causes open loop operation.

Code 44 is set when the O2 sensor signal voltage at the ECM C-D connector terminal "D-7".
^ Remains above 0.2 volt for 60 seconds or more:
^ And the system is operating in closed loop.

CHART TEST DESCRIPTION
1. Grounding the diagnostic terminal with the engine running, enables the "Field Service Mode" and allows the ECM to confirm either open or closed loop operation.

2. A light out or "Open Loop" indicates the fault is present. Disconnecting the 02 sensor will raise the signal voltage above 0.2 volt. If the ECM and wiring are OK, the ECM should recognize the higher voltage, 0.35 to 0.55, and flash open loop when the engine is started.

3. Diagnostic aids:
^ Check for ground in wire between connector and sensor.
^ Sensor. A Mass Air Flow (MAF) sensor Output that causes the ECM to sense a lower than normal air flow will cause the system to go lean. Disconnect the MAF sensor and if the light flashes closed loop (Field Service mode) and the lean condition is gone, replace the MAF sensor.
^ Sensor Wire. Sensor pigtail may be mispositioned and contacting the exhaust manifold.
^ Lean Injectors. Perform cylinder balance test Chart C-2A. Chart C-2A Injector Balance Test
^ Fuel Contamination. Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a lean exhaust and can set a Code 44.
^ EGR. In normal operation, the ECM delivers less fuel and advances spark when EGR comes in. If the EGR does not open, the system will go lean and may have slight spark knock (see Chart C-7) Chart C-7 Exhaust Gas Recirculation (EGR) Check
^ Fuel Pressure. System will be lean if pressure is too low. It may be necessary to monitor fuel pressure while driving the car at various road speeds and/or loads to confirm. See diagnosis Chart A-7A. Chart A-7A Fuel System Diagnosis
^ Exhaust Leaks. If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust and past the sensor.
^ If the above are OK, and the instructions at the top of the chart will set a Code 44, or "CHECK ENGINE' light is "off" more than "on", or flashing "open loop", it is a faulty oxygen sensor.